Search

The anisotropic displacements of selected rigid groups in monoclinic papain have been refined from X-ray diffraction data by application of the rigid-body TLS model. The rigid groups chosen were the aromatic side chains of tryptophan, tyrosine, histidine and phenylalanine, and the planar carboxylic and guanidinium side chains of aspartic acid, glutamic acid, glutamine, asparagine and arginine. The derived translation and libration tensors have been compared with those previously derived for bovine ribonuclease A and provide evidence for different modes and anisotropies of displacement over the two proteins.

Bovine lens gamma IVa-crystallin crystallizes in space group C222(1) with cell dimensions a = 35.1, b = 46.2, c = 186.2 A, and contains one molecule in the asymmetric unit. The structure was determined at 3.0 A resolution using cross-rotation functions and R-factor searches with the bovine lens protein gamma II-crystallin as the model structure. The rotation function appears to be very sensitive to the resolution range and type of coefficient employed; the use of normalized structure-factor amplitudes gave the best results. The potential problem of a pseudo solution due to an internal pseudo-twofold axis was put to advantage by aligning this axis parallel to z. The results of the R-factor search were well defined. The molecular replacement solution was improved by rigid-body least-squares refinement, initially of the whole molecule, then for the two domains. The R factor at this stage was 39.4% at 2.3-10.0 A. The gamma IVa structure has an even higher internal symmetry than gamma II, since the two domains are related by a rotation around the pseudo-twofold axis of 178.7 degrees as compared with 176.2 degrees for gamma II.